This invention relates generally to systems for removing trace pollutants from industrial effluent streams, such as by a sorbent, and more particularly, to a system for removal of such trace pollutants using a modified clay as the sorbent.
There is a clear, generally known need to reduce the level of pollution in the aquatic environment. A significant first step in effecting reduction of the level of such pollution would be achieved by removing trace organic contaminants, such as polychlorinated biphenyls (PCBs), polychlorinated dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs). Such trace organic contaminants are found in industrial effluent water as undesirable by-products of chemical manufacturing. For example, 2,3,7,8-Tetrachlorodioxin (2,3,7,8-TCDD) is formed during the production of 2,4,5-Trichlorophenol, which is an ingredient of many pesticides. Even at extremely low concentrations, 2,3,7,8-TCDD is the most toxic isomer of dioxin and is generally referred to as "Dioxin."
A known, highly advantageous technique for removing trace amounts of organic pollutants in very large volumes of waste water, utilizes a sorbent to which the contaminant is adsorbed. The most commonly used adsorbant today is activated carbon, the production of which utilizes a wide variety of carbonaceous starting materials, such as anthracite and bituminous coal, carbonized shells, peat, etc. The various known methods of activating charcoal can be grouped into two categories. The first category includes chemical activation wherein the carbonaceous materials are impregnated with an activating agent and then pyrolyzed. The second category comprises heat treatment processes wherein chars are heated to temperatures between 350.degree. and 1000.degree. C. in the presence of CO.sub.2, N.sub.2, O.sub.2, HCl, Cl.sub.2, H.sub.2 O and other gases. A portion of the char is burned as the surface area and "activity" of the carbon increases. Modern manufacturing techniques, which include careful monitoring of the activation parameters, yield activated products having high surface areas in a wide range of uniform particle sizes.
In addition to activated charcoal, natural soils and sediments containing various amounts of bound organic carbon or synthetic "zeolite-like" sorbents with specific affinity for rigid, planar aromatic molecules like dioxin have been considered. One known synthetic sorbent is described in U.S. Pat. No. 4,040,990. All of the known systems have significant problems which render them substantially less than ideal for the purpose of removing trace organics from large quantities of water. Activated charcoal and synthetic sorbents are very expensive and therefore do not provide an economical solution to the problem. Natural soils and sediments, however, are less expensive than the activated charcoal and synthetic sorbents, but are not uniform, and in fact exhibit too much variation in binding affinity to be used in large scale technology.
In addition to the systems discussed hereinabove for the disposal of organic pollutants, such as Dioxin, a variety of other methods are known. These include: photolytic dechlorination, microbial degradation, and thermal decomposition. Photolytic dechlorination has been used to detoxify Dioxin-contaminated soil, as well as Dioxin admixed with asphalt and heavy oil. In such situations, the initial concentration of Dioxin was many orders of magnitude higher than is usually present in industrial waste water. For example, the concentration of Dioxin in the contaminated soil, the asphalt, and heavy oil, was in the ppm range, while the concentration in industrial waste water is typically in the ppq range. The process of photolytic dechlorination is disadvantageously characterized by a requirement of high absorption of light photons, and therefore is practical only when high initial concentration of the pollutants is present, and the samples can readily be exposed to light.
As is the case with photolytic dechlorination, the process of microbial degradation also requires the pollutant to be present in high concentration. However, no microorganism has yet been developed which is capable of degrading Dioxin. The process of thermal decomposition requires operating temperatures in excess of 1000.degree. C., and the technology required to implement this process is still in a developmental stage. It is a problem with all three of these processes that they are ineffective when the polluting compound is present in water at extremely low concentrations, illustratively on the order of pptr to ppq.
Swelling clays, generically designated as smectites, have been used widely in the prior art as catalysts, catalyst supports, molecular sieves, adsorbers, and absorbers. The utility of these clays for these purposes is derived from the physical properties of the clay itself. Smectites, such as montmorillonite, have a layered lattice structure in which two-dimensional oxyanions are separated by layers of hydrated cations. The layered structure enable intercalation of layers of a different character between the sheets of the clay structure. In addition, "pillared" clays have been developed wherein intercalated thermally stable cations act as props, or pillars, to support the silicate layers of the clay in the absence of a swelling solvent. The pillar size, or spacing, and hence, the pore size of the clays can be adjusted so as to permit the making of suitable catalysts, catalyst supports, molecular sieves, etc., for various purposes, particularly in the petroleum processing field.
A variety of expanded layer smectite clays, which are based on various cationic species, have been disclosed in the prior art. These include Al, Ti, Fe, Cr, Ni, and Zr. Examples of such clays are described in U.S. Pat. Nos. 4,060,480; 4,176,090, and 4,216,188. The use of inorganic exchange ions to expand smectite layers is described in U.S. Pat. No. 4,060,480. As described in this reference, the clay is treated with hydroxy-aluminum polymers or oligomers in solution, and subsequently the clay is dried and calcined to produce supporting pillars between clay layers. Such pillars serve to maintain the expanded layer state in the clay and leave pores having a rectangular opening configuration, framed by the pillars and the clay layers.
None of the substrates described in the references cited herein are known to be used as compositions which perform as a sorbent for industrial pollutants in an effluent stream. It is to be remembered that the term "adsorption" generally refers to a first step in catalysis and may not necessarily be applicable to the mechanism of a process for removing pollutants from industrial effluents. As is known, a catalyst will adsorb and release. Effluent treatment, however, requires that the composition adsorb the pollutant and retain same.
It is, therefore, an object of this invention to produce an inexpensive system for removing trace organic contaminants which pollute an aquatic environment.
It is also an object of this invention to provide a process for removing trace organic pollutants, typically on the order of between pptr and ppq.
It is another object of this invention to provide a system for removing contaminants from an industrial waste water stream, the contaminants including dioxin, PCBs, PPCDs, and PCDDs.
It is a further object of this invention to provide a material having high sorptive capacity and binding affinity for organic pollutants.
It is still another object of this invention to provide a sorbent material which is inexpensive to use, due to, inter alia, low cost starting materials and high sorptive capacity requiring the use of small quantities of sorbent.
It is yet another object of this invention to provide a process for removing trace organic contaminants which is simple and inexpensive to implement.
It is still a further object of this invention to provide a system for removing trace amounts of contaminants which can be used simply and with existing technology.
It is a still further object of this invention to provide a sorbent material which can easily, and safely, be disposed of after it has been used to remove trace organic pollutants.